Method of producing opaque shadow mark



United States Patent Office 3,441,427 Patented Apr. 29, 1969 3,441,427 METHOD OF PRODUCING OPAQUE SHADOW MARK Bruce D. Skofronick, Appleton, Wis., assignor to Customark Corporation, Appleton, Wis., a corporation of Wisconsin No Drawing. Filed Feb. 7, 1966, Ser. No. 525,343 Int. Cl. D2111 3/36 U.S. Cl. 117-37 6 Claims ABSTRACT OF THE DISCLOSURE A method for producing a sheet of paper having a chemical shadow mark. An area of the paper having a thermosetting curable resin, a curing agent, and an organic solvent is contacted with an aqueous sizing agent before the resin hardens, and the resin is then cured.

This invention relates to a paper article in which the surface contains an opaque area which may be a chemical shadow watermark, or may extend throughout the entire surface area; and the invention also relates to a method for making such paper articles.

Shadow watermarks are those in which the density of the paper fibers in a portion of a sheet of paper is decreased relative to the remaining portions of the paper. Such shadow watermarks are conventionally formed in the papermaking process where a wet web of paper on a Fourdrinier is contacted with a dandy roll having an indented or recessed surface conforming to the design which will be formed on the paper. During such contact the paper fibers accumulate in the recessed or indented surface, and this results in decreased density of paper fibers in that localized area. Such shadow marks tend to be opaque marks which transmit less light relative to the remainder of the paper. The conventional watermark is formed by a reverse procedure in which a dandy roll with a raised design contacts the wet paper to spread the paper fibers and increase their density in that localized area. Such increased density results in the translucents of the typical well-known paper mark.

In issued U.S. Patents Nos. 3,085,898 and 3,140,959 paper articles and method are described wherein chemical translucent watermarks are formed by an economical procedure which obviates the expense and complexity of the conventional watermark formation. It is likewise desirable to obtain a paper article which has a simple and economically produced shadow watermark to obviate the complexity of the conventional watermark formation. It is likewise desirable to obtain a paper article which may be entirely opaqued by a simple and economical process. In a copending application filed concurrently herewith, it was shown how such translucent areas of a thermosetting resin may be rendered opaque by treatment with water. It is desirable to provide additional advantageous ways to make such paper articles as well as new paper articles themselves.

It is a primary object of this invention to provide an article and method whereby opaque areas can be imparted to finished sheets of paper.

Another object is a paper article and method in which opaque areas may be imparted either in a selected design or entirely throughout the article by few manipulative steps in which the surface of a sheet of paper is variously treated to form thereon opaque areas that will be serviceable in generally the same way as the original paper.

Another object is a paper article and method in which a shadow watermark is easily placed on the paper by initially applying a thermosetting resin and curing agent in a selected design to a portion of the paper, and then contacting the paper with a sizing solution without requiring any care to conform the sizing solutions with the first configuration of the design laid onto the surface of the paper.

Another object is a paper article and method in which a paper article is rendered entirely opaque by initially applying a thermosetting resin and curing agent to cover the entire surface, and then contacting the entire paper surface with a sizing solution.

Another object is an article and method in which an opaque area is formed by including a step which simultaneously sizes the paper and participates in forming said opaque area.

Such objects are realized together with other objects which will occur to practitioners who will consider the following disclosure.

For convenience, the process leading to the paper article may be summarized in the following flow diagram:

Impart liquid composition containing thermosetting resin and curing agent therefore to surface of a finished sheet of paper Contact said resin and curing agent with a sizing solution before the resin cures into a hardened form Curing the thermosetting resin with the contacted sizing solution to render the configuration less translucent than the balance of the paper The diagram schematically represents the process which may either be directed to opaquing entire sheets, or a portion in a selected design to obtain a shadow mark known also as a shaded mark or watermark.

U.S. 3,140,959, issued July 14, 1964, teaches how to economically make a paper product with a chemical Watermark by contacting the surface of the paper by means conforming to a selective design, said means having or being wetted with a liquid composition containing a thermosetting resin in an organic solvent. When such composition contacts the paper, that portion of the paper becomes more translucent than the balance of the paper, and such greater translucency is maintained after the thermosetting chemical watermark cures into a hardened form. Such a chemical watermark is firmly adhered to the paper, is ink receptive, and is not removable by ordinary solvents or mechanical eraser means.

The first step in the foregoing flow diagram uses a similar liquid composition containing thermosetting resin and a curing agent, as disclosed in said U.S. 3,140,959. Said resin and curing agent may be referred to herein as impregnating materials. The liquid composition includes organic solvent which, after removal by evaporation, would render the paper translucent in the area of the hard chemical watermark. The liquid composition may be applied to the surface sheet of paper by various means, such as printing, brushing the mark through a stencil, or in other ways. In any event, such an area is manipulated by another step wherein a sizing solution contacts the area before the thermosetting resin in the liquid composition has hardened into what would be the chemically translucent area according to U.S. 3,140,959. After the liquid composition with the impregnating materials contacts a sheet of paper the solvent in the liquid composition begins to immediately absent itself by evaporation. It is preferred that the step of contacting the area of the impregnating materials with the sizing solution occur prior to evaporation of all the solvent. In any event, the important feature is that contact with the sizing solution should occur before the synthetic thermosetting resin cures into a hardened film. Reference may be made to the resin as becoming hard or hardened, and such term is intended to mean the form following an adequate cure of the agent with an appropriate curing agent.

Various sizing solutions are commonly used in the paper, and the most popular are the starch solutions, such as the chlorinated and ethylated starches. Other sizing agents in water solutions include the animal, bone and hide glues. Various equivalent sizing solutions may be used in this step.

Following this step, the resin area has not yet attained its opaque state, or a condition in which such area is less translucent than the original condition of the paper. The last step illustrated in the how diagram requires that the resin area, contacted with a sizing solution, is cured into a hard flow. This curing step is preferably by heating, and this step results in the area becoming opaque, wherein it is less translucent than the remaining portion of the paper. Heating is preferred and not critical because this merely enhances or accelerates the rate of cure. If desired, a room temperature cure could be conducted although extended time periods would be required to accomplish a cure into a desirably hard form. The nature of the interaction between the thermosetting resin and the sizing solution is not known with certainty, but apparently some incompatibility occurs between the Water and the thermosetting resin. Irrespective of the correct explanation, there is obtained a paper article having an opaque area which stands up under mechanical abrasion such as erasing, has excellent ink receptivity, and generally 'has a desirably useful life.

Thermosetting resin of the type disclosed in U.S. 3,140,959 and various curing agents may be used in this process to obtain opaque areas on the paper. These include a melamine and urea formaldehyde, a polyester, a phenol formaldehyde, and the like, as Well as their curing agents.

Particularly successful opaque areas have been obtained by employing an epoxy resin and appropriate curing agent as the impregnating material in the liquid compositions. The liquid composition may have various consistencies, depending on the amounts of the thermosetting resin therein. 'It is required that the consistency be such that it permits handling for applying such liquid composition to the surface of a finished paper. In general, it may be about one-half, more or less, of the liquid composition by weight. The amounts of the thermosetting resin and their cur-ing agents may be variously modified depending on the rate of cure desired, the degree of the hard cure, and the like. By ways of illustration, the liquid composition may be imparted to the paper by using a pick up roll to contact the liquid composition onto a transfer roll and then onto a plate roll which may have an unbroken surface for covering an area equal to the entire sheet, or the surface may have a selected design formed on a material such as a rubber plate. The plate roll contacts the paper web against the backing roll and then the paper web, containing the translucent chemical area, is moved to contacted with the sizing solution.

The sizing solution may be a conventional chlorinated starch and water solution which has been cooked for a sutficient temperature to swell up the starch granules into an operable solution. Various starch concentrations in water may be maintained at moderate temperatures ranging from about room temperature to about 150 F. Such a sizing solution may be in a conventional size tub and the paper web may be moved to such tube to complete the contact of paper and the starch solution. Various equivalent means are known in the art for sizing paper. In addition to a size tub, there are a horizontal size press with puddles, kiss coating, and the like. When referring to sizing herein, reference is intended to surface sizing rather than internal sizing. After the paper web has left the size tub, it may be nipped between rollers to remove the excess starch. It is seen that in this step the entire web of paper is coated with a starch solution so that the paper is simultaneously sized and the translucent impregnating compound is contacted with the starch sizing solution. This leads to an advantageous practice of the process because paper can be conventionally sized while, at the same time, executing a step which leads to opaquing the sheet or forming a shadow chemical Watermark.

The web of paper which has been contacted with the sizing solution has a resin impregnated area which is still more translucent than the remaining portions of the paper. This area is rendered less translucent or opaque relative to the paper by curing the mark which has been contacted with the sizing solution. This can be done in various ways, preferably by heating, such as moving the web of paper over hot dryer rolls which are maintained at temperatures below the level which char or otherwise damage the paper. Various other means may be used in this heating step, such as hot air or infrared heat or the like. while the entire sheet is preferably heated, localized heating of the mark is possible as by a limited stream of hot air, for example.

It is believed that the water content of the sizing solution contributes principally to the reduced light transmission and the raised character of the opaque area. In any event the size agent is part of the opaque area. The light transmission of the opaque area is significantly reduced as measured by the Bausch and Lomb opacimeter, B & L Optical Co., Rochester, N.Y. This reduction is at least about 1% as compared to the light transmission of the original paper. This reduction may vary, and may depend on the particular impregnating materials and the variation within any particular impregnating materials. This reduced light transmission is diametrically opposite to the increased light transmission of a chemical watermark which has not been treated with a sizing solution.

The opaque area is further raised relative to the orig inal surface or thickness of the paper as determined by caliper measurements made with a unit known under the trademark TMl, Model 549M Micrometer Testing Machines, Inc., Mineola, N.Y. The caliper rise is about at least 5% of the original paper, but may rise to about 7%, and even substantially thereover, Again, this may be due to the nature of particular impregnating materials. This rise in caliper of the opaque area is in marked contrast to the chemical transparent area obtained without treatment with the sizing solution. There is substantially no rise in caliper of such a transparent area. It is seen that the opaque area is characterized by a reduced light transmission, a rise, and inclusion of the size agent in the opaque area. The size agent is a part of the opaque area and this is an important feature in view of the advantage of sizing the paper as well as obtaining the opaque area. The size agent does not detract from the desirable properties of the opaque area.

Some examples are presented to illustrate various ways to practice the invention, but such examples are only illustrative, and are not intended as exclusive embodiments.

EXAMPLE I A liquid composition, containing an epoxy impregnating compound is prepared from the following ingredients and amounts- Ingredients: Parts by weight Epoxy resin (Dow Der 332) 5 Epoxy hardener (Dow experimental hardener X-2654.4) 1 Methyl Carbitol (diethylene glycol monomethyl ether) A small metered amount of liquir composition is deposited on the surface of a foot square piece of /2" thick plate glass. The composition is spread uniformly over the surface with a hand roll, consisting of an engraved roll bearing 75 depressions per inch and fitted with a handle. A die or hand stamp of rubberlike material having inscribed on the face thereof a typical watermark design is first pressed against the wet film of the composition on the glass and then stamped on the paper sheet, Before the epoxy resin is cured by the curing agent into a hard film, the sheet of paper is totally immersed in a bath containing 8% chlorinated starch in water, said bath maintained at 80 to 150 F. The sheet of paper is removed and subjected to heating by hot air until the paper is dry.

The Dow 332 epoxy resin and the Dow hardener for said epoxy resin are supplied by the Dow Chemical Company of Midland, Mich. The methyl Carbitol solvent is supplied by Union Carbide.

EXAMPLE 11 Ingredients: Parts by weight Epoxy resin (Dow Der 332) 5 Pyromellitic dianhydride 1 Methyl Carbitol 4 /2 EXAMPLE III Ingredients Parts by weight Dow Der 332 5 Borax epoxy curing agent No. 110 1 Methyl Carbitol 4 /2 The above formulation is manipulated in the same manner as disclosed in Example I to obtain shadow chemical watermarks of desirable properties. The borax curing agent is supplied by the U.S. Borax Company.

EXAMPLE IV Ingredients: Parts by weight Polyester resin (Koplac D-3000-l500) 10.0 Benzoyl peroxide 0.2 Methyl Carbitol 10.2

The polyester resin is supplied by the Kopper Company and the peroxide curing agent by Matherson, Coleman and Bell. The above formulation is manipulated in the same manner as disclosed in Example I to obtain a shadow chemical watermark of desirable properties.

EXAMPLE V Ingredients: Parts by weight Epoxy resin, Epon 812 (Shell Chemical Comp y) 6 Epon curing agent H3 (Shell Chemical Company) 3 Methyl Carbitol 9 The above ingredients are mixed and a portion of a few ml. is deposited at the top of a sheet of paper. A gravure roller of a width wider than the paper is pulled through the deposited liquid composition causing the composition to be laid down on a sheet of dry or finished paper. Within 3 minutes the entire sheet is immersed in a bath containing 8% chlorinated starch and held at to about F. The excess starch solution is removed and the sheet is exposed to a stream of hot air until the sheet is dried and becomes opaque relative to its original condition In like manner the liquid compositions of Examples I through IV are used in the process steps of Example V to opaque entire sheets of paper.

The liquid compositions and steps disclosed in Examples I through V are used with finished paper which is either surface sized previously or not surface sized. An important advantage of the process is that unsurface sized paper may be simultaneously surface sized and rendered opaque. The opaque area, of course, may be limited as for a shadow mark, or may extend throughout the entire surface of the finished paper sheet. A previously sized paper will receive an additional sizing treatment which may cumulative or compleemntary to an original sizing to obtain desired sizing properties.

The paper articles prepared with the chemical shadow watermark are serviceable for at least the useful life of the paper. By this is meant that the shadow watermark is substantially resistant to mechanical abrasion encountered by paper such as erasing. Such is, of course, link receptive in substantially the same way as the remaining portions of the paper, and resists discoloration for at least desirable periods of time. The useful life of paper may be variously measured, and the substantial majority of stationery bond, for example, has a relatively short useful life. Nonetheless, such shadow chemical watermark retains desirable properties even after a stationery bond has been stored or filed for substantial periods. The preferred practice for making shadow marks in the foregoing process called for sizing the entire sheet of the paper, and substantially only that portion may be not necessary since a previously sized paper may be converted into a paper article with the shadow chemical watermark In such a case, the liquid composition with the impregnating materials is imparted to only a portion of the paper, and substantially only that portoin may be contacted with the sizing solution. If desired, previously sized paper could be again contacted in its entirety with the sizing solution.

Reference has been made to sizing solutions and these are intended to include any of the various size tube agents in a water solvent. Understandably, such sizing tube agent will commonly be selected from the starches which are widely used in sizing paper.

Methods for making the paper article of this invention can include the batch and continuous processes. The continuous process will be preferred for large scale production wherein a run of paper web will move through appropriate stations. At a marking station, a web would receive the configuration of the marking formulation. The running web would then pass to a sizing station containing the size tube agent. Contact with this station should be made before an impregnating compound in the marking formulation or liquid composition hardens. As stated, the contact at the size station should be made preferably before substantial portions of the organic solvent are removed from the configuration. The paper web leaving the sizing station will still have a mark which is more translucent, however, the mark becomes more opaque after passing through a curing or heating station. The paper article with the opaque shadow chemical watermark may then be cut into selected dimensions or be otherwise handled,

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of imparting chemical opaque areas to a finished sheet of paper, which comprises the steps of: applying to the surface of said sheet of paper an area of a non-aqueous liquid composition containing a thermosetting curable resin, a curing agent therefore,

and an organic solvent,

contacting said area with a paper sizing solution having a sizing agent in water,

effecting said contact of said sizing solutions with said area before said thermosetting resin therein hardens, and

curing said thermosetting resin on said paper until said thermosetting resin hardens.

2. A method as in claim 1 further characterized in that the sizing solution contains starch as the sizing agent, and the thermosetting resin is an epoxy resin.

3. A method as in claim 1 further characterized in that the sheet of paper is contacted with the liquid composition and the sizing solution so that the paper is sized simultaneously with contacting the liquid composition on said sheet.

4. A method as in claim 1 further characterized in that the liquid composition is applied to the entire sheet of paper, and then the sizing solution is applied to the entire sheet to render the entire sheet opaque.

5. A method as in claim 1 further characterized in that the liquid composition is applied only to a limited portion of the paper surface in a selected design, and then a sizing solution is applied to at least that limited portion to obtain an opaque shadow mark.

6. A paper article produced by the process of claim 1.

References Cited UNITED STATES PATENTS McCorkindale 1621l0 X MacLaurin 162-410 Schroeder 117-155 X Wasserman 1l7-155 X Mackenzie 1l7-38 Vaurio 1l738 Hill 26029.2 X Sommer 260-29.2 X

Pretka 26029.2

Weller 26029.2

Skotromek 117-38 OTHER REFERENCES U.F. Resin Used in Solid-Dot Braille Printing in British Plastics, July 1952, pp. 232434.

John Calkin and George Witharn: Modern Pulp and Paper Making, Reinhold Publishing Corp., New York,

ALFRED L. LEAVITT, Primary Examiner.

ALAN GRIMALDI, Assistant Examiner.

US. Cl. X.R.

l06l9; ll762, 155; 162-ll0, 164

1957, pp. 312-313 and 286-296, 

